The Town of Cortlandt is in the northwest part of the county. The town includes the villages of Buchanan and Croton-on-Hudson.
Commuter service to New York City is available via the Cortlandt train station and the Croton-Harmon Train Station, served by Metro-North Railroad.
US Route 9 passes through the town along the Hudson River side.
According to the United States Census Bureau, the town has a total area of 50.2 square miles (129.9 km²), of which, 39.7 square miles (102.7 km²) of it is land and 10.5 square miles (27.2 km²) of it (20.93%) is water.
There were 13,517 households out of which 39.3% had children under the age of 18 living with them, 64.3% were married couples living together, 7.9% had a female householder with no husband present, and 25.0% were non-families. 21.3% of all households were made up of individuals and 8.8% had someone living alone who was 65 years of age or older. The average household size was 2.75 and the average family size was 3.22.
In the town the population was spread out with 26.5% under the age of 18, 5.3% from 18 to 24, 30.1% from 25 to 44, 25.3% from 45 to 64, and 12.8% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 95.8 males. For every 100 females age 18 and over, there were 92.7 males.
The median income for a household in the town was $75,442, and the median income for a family was $89,053. Males had a median income of $59,949 versus $41,115 for females. The per capita income for the town was $33,432. About 2.9% of families and 4.5% of the population were below the poverty line, including 4.1% of those under age 18 and 5.1% of those age 65 or over.